Switching elements in an inverter main circuit are responsive to switching control signals. Phase voltages are applied to a polyphase load via the switching elements. Basic voltage command values are generated for phases of the polyphase load respectively. The basic voltage command values are converted into final voltage command values respectively. During a time interval for which at least two of the basic voltage command values are approximately equal to each other, the final voltage command values corresponding to the two of the basic voltage command values are equal to one of a maximum and a minimum. A carrier wave is subjected to pulse-width modulation responsive to the final voltage command values to produce the switching control signals. The produced switching control signals are outputted to the switching elements in the inverter main circuit.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A power converter apparatus comprising: an inverter main circuit including 1) switching elements responsive to switching control signals, and 2) means for applying phase voltages to a polyphase load via the switching elements; command value outputting means for outputting basic voltage command values for phases of the polyphase load respectively; command value converting means for converting the basic voltage command values outputted by the command value outputting means into final voltage command values respectively, wherein during a time interval for which at least two of the basic voltage command values are approximately equal to each other, the final voltage command values corresponding to said two of the basic voltage command values are equal to one of a maximum and a minimum; and control signal outputting means for subjecting a carrier wave to pulse-width modulation responsive to the final voltage command values generated by the command value converting means to produce the switching control signals, and for outputting the switching control signals to the switching elements in the inverter main circuit.
2. A power converter apparatus as recited in claim 1, wherein the command value converting means comprises means for equalizing at least one of the final voltage command values which is of a phase different from conversion object phases to a mean of inter-line voltages with the basic voltage command values of the conversion object phases.
3. A power converter apparatus as recited in claim 1, wherein the polyphase load comprises a polyphase AC motor.
4. A power converter apparatus as recited in claim 3, wherein the polyphase AC motor comprises a three-phase AC motor.
5. A power converter apparatus comprising: an inverter main circuit including 1) switching elements responsive to switching control signals, and 2) means for applying phase voltages to a polyphase load via the switching elements; command value outputting means for outputting basic voltage command values for phases of the polyphase load respectively; command value converting means for converting the basic voltage command values outputted by the command value outputting means into final voltage command values respectively, wherein a time interval for which at least two of the basic voltage command values are approximately equal to each other includes an alternation of first conversion time intervals and second conversion time intervals, wherein during each of the first conversion time intervals, the final voltage command values corresponding to said two of the basic voltage command values are equal to one of a maximum and a minimum, and wherein during each of the second conversion time intervals, only one of the final voltage command values corresponding to said two of the basic voltage command values is equal to one of the maximum and the minimum; and control signal outputting means for subjecting a carrier wave to pulse-width modulation responsive to the final voltage command values generated by the command value converting means to produce the switching control signals, and for outputting the switching control signals to the switching elements in the inverter main circuit.
6. A power converter apparatus as recited in claim 5, wherein the command value converting means comprises means for setting a period of the alternation of the first conversion time intervals and the second conversion time intervals to an integer times a period of the carrier wave.
7. A power converter apparatus as recited in claim 5, wherein during each of the second conversion time intervals, said only one of the final voltage command values corresponds to one of the basic voltage command values which is maximum in inter-line voltage with another of the basic voltage command value.
8. A power converter apparatus as recited in claim 5, wherein the command value converting means comprises: means for setting a length of the second conversion time intervals to a positive real number n times a length of the first conversion time intervals; means for, during each of the first conversion time intervals, subjecting at least one of the final voltage command values which is of a phase different from conversion object phases to level shift to maintain an inter-line voltage with the basic command voltage value of a conversion object phase in each of the second conversion time intervals; and means for, during each of the second conversion time intervals, subjecting one of the final voltage command values which is of a conversion object phase only for each of the first conversion time intervals to level shift to multiply an inter-line voltage with the basic voltage command value of a conversion object phase in each of the second conversion time intervals by (1+1/n).
9. A power converter apparatus as recited in claim 8, wherein the command value converting means comprises means for setting the positive real number n to 1.
10. A power converter apparatus as recited in claim 5, wherein the command value converting means comprises means for increasing a length of the second conversion time intervals relative to the first conversion time intervals as a difference between the basic voltage command values of conversion object phases in the first conversion time intervals increases.
11. A power converter apparatus as recited in claim 5, wherein the polyphase load comprises a three-phase load.
12. A power converter apparatus comprising: an inverter main circuit including 1) switching elements responsive to switching control signals, and 2) means for applying phase voltages to a polyphase load via the switching elements; command value outputting means for outputting basic voltage command values for phases of the polyphase load respectively; command value converting means for comparing the basic voltage command values outputted by the command value outputting means, and for converting the basic voltage command values into final voltage command values respectively in response to results of said comparing, wherein during a specified time interval containing a time point at which at least two of the basic voltage command values are equal, the final voltage command values corresponding to said two of the basic voltage command values are equal to one of a maximum and a minimum; and control signal outputting means for subjecting a carrier wave to pulse-width modulation responsive to the final voltage command values generated by the command value converting means to produce the switching control signals, and for outputting the switching control signals to the switching elements in the inverter main circuit.
13. A power converter apparatus as recited in claim 1, wherein the basic voltage command values are based on amplitude variations of sinusoidal waves.
14. A method of controlling drive of a polyphase load, comprising the steps of: applying phase voltages to the polyphase load via switching elements in an inverter main circuit; generating basic voltage command values for phases of the polyphase load respectively; converting the basic voltage command values into final voltage command values respectively, wherein during a time interval for which at least two of the basic voltage command values are approximately equal to each other, the final voltage command values corresponding to said two of the basic voltage command values are equal to one of a maximum and a minimum; subjecting a carrier wave to pulse-width modulation responsive to the final voltage command values to produce switching control signals; and outputting the switching control signals to the switching elements in the inverter main circuit.
15. A method as recited in claim 14, further comprising the step of equalizing at least one of the final voltage command values which is of a phase different from conversion object phases to a mean of inter-line voltages with the basic voltage command values of the conversion object phases.
16. A method as recited in claim 14, wherein the polyphase load comprises a polyphase AC motor.
17. A method as recited in claim 16, wherein the polyphase AC motor comprises a three-phase AC motor.
18. A method of controlling drive of a polyphase load, comprising the steps of: applying phase voltages to the polyphase load via switching elements in an inverter main circuit; generating basic voltage command values for phases of the polyphase load respectively; converting the basic voltage command values into final voltage command values respectively, wherein a time interval for which at least two of the basic voltage command values are approximately equal to each other includes an alternation of first conversion time intervals and second conversion time intervals, wherein during each of the first conversion time intervals, the final voltage command values corresponding to said two of the basic voltage command values are equal to one of a maximum and a minimum, and wherein during each of the second conversion time intervals, only one of the final voltage command values corresponding to said two of the basic voltage command values is equal to one of the maximum and the minimum; subjecting a carrier wave to pulse-width modulation responsive to the final voltage command values to produce switching control signals; and outputting the switching control signals to the switching elements in the inverter main circuit.
19. A method as recited in claim 18, further comprising the step of setting a period of the alternation of the first conversion time intervals and the second conversion time intervals to an integer times a period of the carrier wave.
20. A method as recited in claim 18, wherein during each of the second conversion time intervals, said only one of the final voltage command values corresponds to one of the basic voltage command values which is maximum in inter-line voltage with another of the basic voltage command value.
21. A method as recited in claim 18, further comprising the steps of: setting a length of the second conversion time intervals to a positive real number n times a length of the first conversion time intervals; during each of the first conversion time intervals, subjecting at least one of the final voltage command values which is of a phase different from conversion object phases to level shift to maintain an inter-line voltage with the basic command voltage value of a conversion object phase in each of the second conversion time intervals; and during each of the second conversion time intervals, subjecting one of the final voltage command values which is of a conversion object phase only for each of the first conversion time intervals to level shift to multiply an inter-line voltage with the basic voltage command value of a conversion object phase in each of the second conversion time intervals by (1+1/n).
22. A method as recited in claim 21, further comprising the step of setting the positive real number n to 1.
23. A method as recited in claim 18, further comprising the step of increasing a length of the second conversion time intervals relative to the first conversion time intervals as a difference between the basic voltage command values of conversion object phases in the first conversion time intervals increases.
24. A method as recited in claim 18, wherein the polyphase load comprises a three-phase load.
25. A method of controlling drive of a polyphase load, comprising the steps of: applying phase voltages to the polyphase load via switching elements in an inverter main circuit; generating basic voltage command values for phases of the polyphase load respectively; comparing the basic voltage command values; converting the basic voltage command values into final voltage command values respectively in response to results of said comparing, wherein during a specified time interval containing a time point at which at least two of the basic voltage command values are equal, the final voltage command values corresponding to said two of the basic voltage command values are equal to one of a maximum and a minimum; subjecting a carrier wave to pulse-width modulation responsive to the final voltage command values to produce switching control signals; and outputting the switching control signals to the switching elements in the inverter main circuit.
26. A method as recited in claim 14, wherein the basic voltage command values are based on amplitude variations of sinusoidal waves.
27. A power converter apparatus comprising: an inverter main circuit including 1) switching elements responsive to switching control signals, and 2) means for applying phase voltages to a polyphase load via the switching elements; command value outputting means for outputting basic voltage command values for phases of the polyphase load respectively; command value converting means for converting the basic voltage command values outputted by the command value outputting means into final voltage command values respectively, wherein a specified time interval for which at least two of the basic voltage command values are approximately equal to each other includes an alternation of first conversion time intervals and second conversion time intervals, wherein during each of the first conversion time intervals, the final voltage command values corresponding to said two of the basic voltage command values are equal to one of a maximum and a minimum, and wherein during each of the second conversion time intervals, only one of the final voltage command values corresponding to said two of the basic voltage command values is equal to one of the maximum and the minimum; phase changing means for changing a phase of the specified time interval used by the command value converting means; and control signal outputting means for subjecting a carrier wave to pulse-width modulation responsive to the final voltage command values generated by the command value converting means to produce the switching control signals, and for outputting the switching control signals to the switching elements in the inverter main circuit.
28. A power converter apparatus as recited in claim 27, wherein the phase changing means comprises means for detecting a phase difference between a phase of one of the basic voltage command values and a phase of a corresponding output current flowing into the polyphase load from the inverter main circuit, and means for changing the phase of the specified time interval in response to the detected phase difference.
29. A power converter apparatus as recited in claim 28, wherein the phase changing means comprises means for changing the phase of the specified time interval so that a time position different from one of a maximum and a minimum of one of the final voltage command values coincides with a zero-cross point of a corresponding output current flowing into the polyphase load from the inverter main circuit.
30. A power converter apparatus as recited in claim 27, wherein the phase changing means comprises means for detecting a phase difference between a phase of one of the basic voltage command values and a phase of a current command value fed from an external, and means for changing the phase of the specified time interval in response to the detected phase difference.
31. A power converter apparatus as recited in claim 30, wherein the polyphase load comprises a three-phase load, and the phase changing means comprises means for changing the phase of the specified time interval so that a time position different from one of a maximum and a minimum of one of the final voltage command values coincides with a zero-cross point of a corresponding current command value.
32. A power converter apparatus as recited in claim 27, wherein the polyphase load comprises a polyphase AC motor.
33. A power converter apparatus as recited in claim 27, wherein the command value converting means comprises: means for setting a length of the second conversion time intervals to a positive real number n times a length of the first conversion time intervals; means for, during each of the first conversion time intervals, subjecting at least one of the final voltage command values which is of a phase different from conversion object phases to level shift to maintain an inter-line voltage with the basic command voltage value of a conversion object phase in each of the second conversion time intervals; and means for, during each of the second conversion time intervals, subjecting one of the final voltage command values which is of a conversion object phase only for each of the first conversion time intervals to level shift to multiply an inter-line voltage with the basic voltage command value of a conversion object phase in each of the second conversion time intervals by (1+1/n).
34. A power converter apparatus as recited in claim 33, wherein the phase changing means comprises means for changing the phase of the specified time interval so that the final voltage command values are limited to within a predetermined non-overmodulation range during the second conversion time intervals.
35. A method of controlling drive of a polyphase load, comprising the steps of: applying phase voltages to the polyphase load via switching elements in an inverter main circuit; generating basic voltage command values for phases of the polyphase load respectively; converting the basic voltage command values into final voltage command values respectively, wherein a time interval for which at least two of the basic voltage command values are approximately equal to each other includes an alternation of first conversion time intervals and second conversion time intervals, wherein during each of the first conversion time intervals, the final voltage command values corresponding to said two of the basic voltage command values are equal to one of a maximum and a minimum, and wherein during each of the second conversion time intervals, only one of the final voltage command values corresponding to said two of the basic voltage command values is equal to one of the maximum and the minimum; changing a phase of the specified time interval; subjecting a carrier wave to pulse-width modulation responsive to the final voltage command values to produce switching control signals; and outputting the switching control signals to the switching elements in the inverter main circuit.
36. A method as recited in claim 35, wherein the phase changing step comprises detecting a phase difference between a phase of one of the basic voltage command values and a phase of a corresponding output current flowing into the polyphase load from the inverter main circuit, and changing the phase of the specified time interval in response to the detected phase difference.
37. A method as recited in claim 36, wherein the phase changing step comprises changing the phase of the specified time interval so that a time position different from one of a maximum and a minimum of one of the final voltage command values coincides with a zero-cross point of a corresponding output current flowing into the polyphase load from the inverter main circuit.
38. A method as recited in claim 35, wherein the phase changing step comprises detecting a phase difference between a phase of one of the basic voltage command values and a phase of a current command value fed from an external, and changing the phase of the specified time interval in response to the detected phase difference.
39. A method as recited in claim 38, wherein the phase changing step comprises changing the phase of the specified time interval so that a time position different from one of a maximum and a minimum of one of the final voltage command values coincides with a zero-cross point of a corresponding current command value.
40. A method as recited in claim 35, wherein the polyphase load comprises a polyphase AC motor.
41. A method as recited in claim 35, further comprising the steps of: setting a length of the second conversion time intervals to a positive real number n times a length of the first conversion time intervals; during each of the first conversion time intervals, subjecting at least one of the final voltage command values which is of a phase different from conversion object phases to level shift to maintain an inter-line voltage with the basic command voltage value of a conversion object phase in each of the second conversion time intervals; and during each of the second conversion time intervals, subjecting one of the final voltage command values which is of a conversion object phase only for each of the first conversion time intervals to level shift to multiply an inter-line voltage with the basic voltage command value of a conversion object phase in each of the second conversion time intervals by (1+1/n).
42. A method as recited in claim 41, wherein the phase changing step comprises changing the phase of the specified time interval so that the final voltage command values are limited to within a predetermined non-overmodulation range during the second conversion time intervals.
43. A power converter apparatus as recited in claim 5, wherein the command value converting means comprises means for changing a length of the second conversion time intervals relative to the first conversion time intervals.
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December 20, 2000
November 27, 2001
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